The photochemical reaction between alcohols and oxygen sensitized by quinone catalysts has been studied for a number of years. For example, Tickle and Wilkinson.sup.1 studied the photooxidation of isopropanol (2-propanol) using anthraquinone (AQ) as a catalyst. The overall stoichiometry of the reaction is ##STR1## The mechanism is proposed to involve the photoreduction of AQ via its triplet State to form anthrahydroquinone which is converted back to the starting catalyst AQ with air or oxygen with the concurrent formation of HOOH.
An analogous reaction involving the catalytic reduction of an alkyl anthraquinone by hydrogen is the basis of a current industrial synthesis of hydrogen peroxide (HOOH) via the reaction sequence ##STR2## where R.sub.1 and R.sub.2 can be hydrogen or C.sub.1 -C.sub.20 alkyl groups
Hydrogen peroxide is an important industrial chemical. It is widely used as a bleach, e.g. in the pulp and paper industry. It is also used extensively in the mining industry, e.g, for removing cyanide residues from gold mining operations. It is basically an environmentally acceptable chemical, unlike many competitive industrial bleaching compounds. Hydrogen peroxide is however a difficult material to transport safely. The locations where it is to be used industrially, e.g. mining sites and pulp mills, are often far removed from other chemical manufacturing and processing facilities. The production of the required hydrogen peroxide on site is accordingly desirable.
AQ derivatives are widely used in industrial process for the production of hydrogen peroxide. The AQ derivative is hydrogenated to anthrahydroquinone (AHQ), which is subsequently oxygenated to AQ and hydrogen peroxide. Separation of the AQ from the product is complicated and costly. Liquid-liquid extraction, to take out the hydrogen peroxide product as an aqueous solution, is necessary. This is costly, and involves large volumes of recycle. Quantitative separation is not achieved. Only dilute solutions of hydrogen peroxide are obtained, unless subsequent distillation is undertaken.
It is an object of the present invention to provide novel methods of conducting anthraquinone-catalyzed chemical processes, which overcome or at least reduce one or more of the aforementioned disadvantages.
It is a further object to provide a novel process for production of hydrogen peroxide.